exists                 package:base                 R Documentation

_I_s _a_n _O_b_j_e_c_t _D_e_f_i_n_e_d?

_D_e_s_c_r_i_p_t_i_o_n:

     Search for an R object of the given name on the search path.

_U_s_a_g_e:

     exists(x, where = -1, envir = , frame, mode = "any", inherits = TRUE)

_A_r_g_u_m_e_n_t_s:

       x: a variable name (given as a character string).

   where: where to look for the object (see the details section); if
          omitted, the function will search, as if the name of the
          object appeared in unquoted in an expression.

   envir: an alternative way to specify an environment to look in, but
          it's usually simpler to just use the 'where' argument.

   frame: a frame in the calling list.  Equivalent to giving 'where' as
          'sys.frame(frame)'.

    mode: the mode of object sought.

inherits: should the enclosing frames of the environment be inspected.

_D_e_t_a_i_l_s:

     The 'where' argument can specify the  environment in which to look
     for the object in any of several ways: as an integer (the position
     in the 'search' list); as the character string name of an element
     in the search list; or as an 'environment' (including using
     'sys.frame' to access the currently active function calls). The
     'envir' argument is an alternative way to specify an environment,
     but is primarily there for back compatibility.

     This function looks to see if the name 'x' has a value bound to
     it. If 'inherits' is 'TRUE' and a value is not found for 'x', then
     the parent frames of the environment are searched until the name
     'x' is encountered.  *Warning:* This is the default behaviour for
     R but not for S.

     If 'mode' is specified then only objects of that mode are sought.
     The function returns 'TRUE' if the variable is encountered and
     'FALSE' if not.

     The 'mode' includes collections such as '"numeric"' and
     '"function"': any member of the collection will suffice.

_V_a_l_u_e:

     Logical, true if and only if the object is found on the search
     path.

_R_e_f_e_r_e_n_c_e_s:

     Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) _The New S
     Language_. Wadsworth & Brooks/Cole.

_S_e_e _A_l_s_o:

     'get'.

_E_x_a_m_p_l_e_s:

     ##  Define a substitute function if necessary:
     if(!exists("some.fun", mode="function"))
      some.fun <- function(x) { cat("some.fun(x)\n"); x }
     search()
     exists("ls", 2) # true even though ls is in pos=3
     exists("ls", 2, inherits=FALSE) # false

